A lightning strike destroyed a paddock killing six ancient breed horses and their foals.
One of the dead was a foal crushed by its mother when she was felled by the bolt while suckling the youngster.
A seventh horse - a two-year-old colt - is still missing after the storm in central Italy on June 3.
The herd of rare Catria mares was struck by lightning as the storm raged above their field near Cagli, in Pesaro and Urbino province.
The sturdy, small horses have been bred in the region for generations and are highly valued by mountain farmers for their sure-footedness over rough land.
Local media reported that three mares and three foals died in the storm.
Expert Mirco Ravaioli - who heads a local Catria club - said a search to find the missing colt in a 500-hectare estate of pastures and woods is underway.
Meanwhile, one lost foal - born just days before the storm - was found unharmed and returned to the herd.
The six dead horses were discovered by a team of firefighters who had been called in to evacuate a group of around 20 tourists from a mountain refuge.
Regional official Damiano Bartocetti told local media: "Of the five, one small foal was crushed under its mother's belly. She was probably nursing it.
"We will carry out a wider inspection of the area to check for the possible presence of other animals."
He added: "The rescuers had a very busy day, with their operations ending late in the evening.
"The priority was to secure the tourists and close the access roads."
The Catria horse - or Cavallo del Catria - originates from the picturesque mountainous region of Monte Catria in the central Apennines, Marche region.
Records show it was being sold to nobility and used to stock the cavalries of surrounding regions more than 1,000 years ago.
Catria horses are recognised in Italy as one of the 15 indigenous horse breeds with limited distribution by the Italian Breeders' Association, AIA.
